1. Field of the Invention P The invention relates to a process for making it possible to replace the hydraulic fluid contained in a possibly complex control circuit such as a hydraulic control circuit of an aircraft.
2. Description of the Prior Art
Although the process according to the invention is particularly suitable for the replacement of the hydraulic fluid contained in the hydraulic control circuits of aircraft,, it can also be used in numerous other technical fields without passing outside the scope of the invention.
A hydraulic control circuit generally includes a tank in which the hydraulic fluid is stored under pressure. The hydraulic fluid contained in the tank is sampled or tapped by one or more pumps through a suction branch and is then delivered under pressure to each of the control means of the circuit by a delivery branch, before being returned to the tank by a low pressure return branch.
In complex hydraulic control circuits such as those equipping aircraft, one or more high pressure filters are placed in the delivery branch. Moreover, a general filter is placed in the return branch immediately upstream of the tank.
The presence of one or more filters in the hydraulic control circuits makes it possible to filter any particles present in the hydraulic fluid Consequently the pollution of said fluid by solid particles is maintained within acceptable limits. Moreover, in the particular case of circuits equipping aircraft, a ground connection system makes it possible to connect the circuits to an external filtering installation designed for eliminating this type of pollution.
However, these filtration means have no effect in the case of a chemical pollution of the hydraulic fluid contained in the circuit. Such a pollution can be caused by the introduction into the circuit of an incompatible fluid, acid formation or overheating leading to the deterioration of the characteristics of the fluid.
When such a chemical pollution occurs, only a complete change of the hydraulic fluid contained in the circuit restores the quality of said fluid. It may also prove necessary to replace the fluid present in the circuit in order to change the fluid type used.
In both cases, the replacement of the hydraulic fluid contained in the circuit can at present not take place without having recourse to at least one of two existing processes.
A first of these processes comprises of emptying the tank, filling it with the new fluid, operating the control means and repeating this cycle several times. It is clear that this process only permits a partial replacement of the hydraulic fluid. Moreover, a satisfactory replacement of the fluid can only be obtained by multiplying the number of cycles.
Another known process for emptying the hydraulic fluid contained in the control circuit comprises of emptying the tank and disconnecting the pipes forming the circuit at several locations, so as to bring about a sectionwise elimination of the spent hydraulic fluid. However, this method leads to the introduction of air and particle-type pollution into the circuit It can also lead to leaks or to the forgetting to reconnect all the pipes.